A prolactin test is a blood test used to measure the levels of the hormone prolactin in the body. Prolactin is a hormone that is primarily responsible for the production of breast milk in women after childbirth, but it also has other functions in both men and women, including regulating the immune system and reproductive function. The test is usually ordered by a healthcare provider if there are concerns about abnormal menstrual periods, infertility, or breast milk production. It may also be ordered if there are symptoms of a prolactinoma, a type of pituitary tumor that can cause overproduction of prolactin. A prolactin test is a simple and safe procedure that can provide valuable information about a person’s hormone levels and overall health.